A heat curable elastomer or gel composition mainly composed of a polymer having at least two alkenyl groups per molecule and a perfluoro polyether backbone gives a cured product which is highly resistant to heat, chemicals, solvents and water. The cured product also has a good releasing property and, naturally, does not adhere to a substrate well.
To improve adhesion of the aforesaid compositions without sacrificing their good properties, a primer may be applied to a substrate before applying the compositions.
Various primers are commercially available, for example, a silane primer mainly composed of a silane coupling agent, and a primer mainly composed of a polymer such as a synthetic rubber, acrylic resin, urethane resin, or epoxy resin. However, these primers do not bond the aforesaid heat curable elastomer or gel composition satisfactorily because they have poor affinity with the composition, so that they do now wet the compositions well at the interface between the primer and the composition.
A heat curable fluorinated elastomer and a heat curable fluorinated elastomer gel compositions are known which have improved adhesion by containing components which function like primers.
For example, Japanese Patent Application Laid-Open No. H9-95615 discloses a heat curable fluorinated composition comprising (A) a fluorine-containing amide compound having vinyl groups at both ends and a perfluoropolyether backbone, (B) a fluorine-containing organohydrogensiloxane having at least one perfluoroxyalkyl, perfluoroalkyl, perfluoroxyalkylene or perfluoroalkylene group and two hydroxysilyl group per molecule, (C) a catalytic amount of a platinum metal compound, and (D) an organosiloxane having at least one epoxy group and/or trialkoxysilyl group bonded to a silicon atom via a carbon atom or a carbon atom and an oxygen atom. A cured product is resistant to solvent, chemicals, heat and a low temperature and humidity. Further, by heating at a relatively low temperature for a relatively short period of time, the composition gives a cured product strongly adhered to a metal or plastic.
Japanese Patent Application Laid-Open No. 2001-72868 discloses a curable fluorinated elastomer composition comprising, in addition to the aforesaid components (A) to (D), a carboxylic acid anhydride. Cured composition adheres well to various kinds of substrates, especially to PPS and polyamide and therefore useful as an adhesive for articles such as a case made of PPS or polyamide.
Japanese Patent Application Laid-Open No. 2002-105319 discloses a curable composition comprising, in addition to the aforesaid components (A) to (D), (E) an organosiloxane having at least one SiH bond, at least one cyclic carboxylic acid anhydride residue bonded to a silicon atom via a carbon atom, or at least one perfluoroxyalkyl group or perfluoroalkyl group bonded to a silicon atom via a carbon atom per molecule. Cured composition adheres well to various kinds of substrates, especially to PPS, polyamide, and polyimide and therefore useful as an adhesive for articles such as automobile parts, electric or electronic parts made of these plastic.
Japanese Patent Application Laid-Open No. 2002-194220 discloses a curable gel composition which strongly adheres to a substrate when cured. The composition comprises, in addition to the aforesaid components (A) to (D), (E) a carboxylic acid anhydride. Cured composition, which is a fluorinated gel, adheres well to various kinds of substrates, especially PPS and PBT and therefore useful as adhesive for articles such as a case made of PPS or PBT.
The aforesaid heat curable elastomer or gel compositions can be bonded to various substrates such as metals, glass, ceramics and plastics, by containing adhesion-enhancing components having an alkoxysilyl group, an epoxy group, a carboxyl group or acid anhydride residue.
However, these adhesion-enhancing components, when contained in a fluorinated elastomer, tend to degrade mechanical strength or compression permanent set of the elastomer. In a heat curable fluorinated gel, these components tend to change hardness, determined by penetration of a needle, of a cured product with time, indicating that the cured product hardens to be more brittle.